BAGHDAD/BEIRUT: Iraqi forces recaptured territory from advancing Islamic State militants near the recently-fallen city of Ramadi on Sunday, while in Syria the government said the Islamists had killed hundreds of people since capturing the town of Palmyra.

The fall of Ramadi and Palmyra, on opposite ends of the vast territory controlled by Islamic State fighters, were the militant group's biggest successes since a U.S.-led coalition launched an air war to stop them last year.

The near simultaneous victories against the Iraqi and Syrian armies have forced Washington to examine its strategy, which involves bombing from the air but leaving fighting on the ground to local forces in both countries.

In a sharp criticism of Washington's ally, U.S. Defense Secretary Ashton Carter accused Iraq's army of abandoning Ramadi, a provincial capital west of Baghdad, to a much smaller enemy force.

"The Iraqi forces just showed no will to fight," he told CNN's State of the Union programme. "They vastly outnumbered the opposing force, and yet they withdrew from the site."

Iraq's government, along with Iran-backed Shi'ite militiamen and locally-recruited Sunni tribal fighters, launched a counter-offensive on Saturday, a week after losing Ramadi. A police major and a pro-government Sunni tribal fighter in the area said they had retaken the town of Husaiba al-Sharqiya, about 10 km (6 miles) east of Ramadi.